Analysis of saline effluent dispersion and transport around an engineered beach development project

Author: Eric C. Cruz, Rachel B. Francisco, Clint Chester M. Reyes

Presenter: Eric C. Cruz

Saline effluents are increasingly being discharged into the sea as desalination technologies continue to improve and are increasingly being used for water supply in coastal communities and beach development industry. A desalination plant is typically installed inland which processes out potable water from a continuous inflow of seawater. and subsequently discharges the resulting saline effluent into the sea. Ideally the effluent is discharged where the ambient currents are strong enough to disperse the amplified saline inflow. In a developed beach coast, the discharge location is a paramount consideration owing to the fact that: (1) incomplete dispersion will undesirably stagnate highly saline effluent; (2) partially dispersed effluent can re-circulate back into the beach interior; and (3) the flushing action of the beach interior by tidal currents can be impeded by an ill-located discharge outfall.

This paper studies the dispersion and transport of a saline effluent discharge (SED) into the nearshore zone of an engineered beach coast. The coast is protected from wave attack by a layout of breakwaters and the location of the saline outfall is based on the inland location of the desalination plant. The dispersion and transport of SED in the nearshore zone is governed by the transport equation:

The simulative analysis is applied to a developed beach coast where 2 possible locations of SED release are being mulled. Table 1 summarizes the properties of the SED. During an Amihan month under the influence of tidal currents, Figure 2 shows chronological snapshots of the salinities due to a SED release at a northern location. Time motion analysis of the dispersion patterns for this location yields a resurgence time of about 6 hours during spring tide and about 4 hours during neap tide. 

The simulative methodology in this paper can be applied to determine a suitable location for SED outfall that meets the regulatory or operational thresholds for discharged salinities. The study shows that the location of the SED outfall must be determined such that the dispersion and transport optimizes the flushing capability of nearshore currents.


First National Scientific Conference on Water, 2019 November 7-9

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